a mastermind solver

mastermindsolver.pl

#!/usr/bin/perl
 
sub generate {
   return int(rand() * 6 + 1) . int(rand() * 6 + 1) . int(rand() * 6 + 1) . int(rand() * 6 + 1);
}
 
$solution=generate();

for ($x1 = 1 ; $x1 < 7 ; $x1++) {
    for ($x2 = 1 ; $x2 < 7 ; $x2++) {
        for ($x3 = 1;$x3 < 7;$x3++) {
            for ($x4 = 1 ; $x4 < 7 ; $x4++) {
                $possible{"$x1$x2$x3$x4"}=1;
            }
        }
    }
}

$guess="1111";
 
while (evaluate($guess,$solution) ne "BBBB") {
    $matches=evaluate($guess,$solution);
    print "$guess $matches " . (scalar keys %possible) . " \n";
    foreach $possible (keys %possible) {
        if (evaluate($guess,$possible) ne $matches) {
            delete $possible{$possible};
        }
    }
    $guess=(sort keys %possible)[0];
}
 
print "$guess " . evaluate($guess,$solution) . "\n";
 
sub evaluate {
    my $guess=shift; my $solution=shift;
    my $black=0;
    my $white=0;
    my $result="";
    for ($i=0;$i<4;$i++) {
        if (substr($solution,$i,1) eq substr($guess,$i,1)) {
            $result.="B";
            substr($guess,$i,1)="0";
            substr($solution,$i,1)="0";
        }
    }
    for ($i = 1 ; $i <= 6; $i++) {
        $result .= "W"x(min($solution =~ s/$i//g,$guess =~ s/$i//g));
    }
    return $result;
}
 
 
sub min {
    my $i=eval shift;
    my $j=eval shift;
    return ($i < $j) ? $i : $j;
}